Another reason popular superstitions work is because of their religious or faith-based origins. You could be practicing a superstition without even realizing that you're appealing to God or another divine spirit. By invoking certain superstitious beliefs, you're actually praying. There's plenty of proof that prayer works and there's proof that superstitions do too. Here's a superstitions list that covers the most popular superstitions.
Knocking on Wood»